A senpai and kohai are generally similar in a lot of ways. They’re usually fairly close in age, and have a similar occupation and social standing.The differences is when it comes to seniority and/or experience.

A downclass man or woman associated with trying to get senpai to notice them and will stop at nothing to get their attention.

someone who you have a crush on but the same age

Someone who you have a crush on that is younger than you.

Kohai is slang for an underage Japanese male with a huge dong.